Engine-driven generator



y 9. 1930. F. H. PRITCHARD 1,111 938 ENGINE DRIVEN GENERATOR Filed Jan. 1'7, 1928 Inventor Franklin HPritchard His Attorney Patented July 29, 1930 UNITED STATES PATENT OFFICE I H. mm, 01' 1mm, PENNSYLVANIA, ASSIGNOB TO GENERAL ELEC- TRIO OOIPANY, A'OORPOBATION OF NEW YORK ENGINE-DRIVEN GENERATOR Application filed January 17, 1928. Serial No. 247,418.

My invention relates to engine driven generators, and more particularly to an arrangement for preventing a decrease in the speed of the engine below the speed at which it develops maximum war.

In vehicles employing electric driving motors which receive power from an engine driven generator, in starting and'in passing over steep ades the current demand of the motors is such that the engine is overloaded. which causes a substantial decrease in its speed. It is well known that these engines produce a maximum power output at a definite speed and the generator is so designed that the engine will run at this speed at full load. As a result, when the current demand of the driving motors overloads the generator the engine is reduced in speed so that the power developed thereby is reduced, tending to stall the engine.

The object of my invention is to provide an arrangement which varies the voltage of the generator in response to a decrease in speed of the engine so that the latter will in crease to its normal speed at which its ower. output is a maximum. I accomplish t 's by the use of a centrifugal device which quickly and positively decreases the voltage of the generator in response to a decrease in speed of the driving means. This enables me to minimize slowing down of the engine upon overloading of the generator and to operate the engine at maximum power during periods of overload on the generator.

My invention will be more fully set forth in the following description referring to the accompanying drawing and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed'to and forming a part of this specification.

In the drawing the single figure is a diagrammatic view of an internal combustion engine driven generator set embodying my invention.

Referring to the drawing, the engine driven generator set in connection with which I have shown my invention is of the type ordinarily employed in vehicles such. as passenger busses and trucks, although it may be used in vehicles of other types such, for example, as railway cars or locomotives.- This engine driven generator set comprises an internal combustion engine 10 which is connected by a drive shaft 11 to an electric generator 12 adapted'to supply power to driving motors 13 connected to the vehicle wheels. The engine is provided with a throttle 14 having the usual manual control lever 14, and the generator is provided with an excitation system including afield exciting winding 15 and a variable resistance 16 for adjusting the voltage of the enerator.

For an particular throttle setting if the load on t e drivin motors is increased, as in passing up a gra e, the load on the generator may become greater than the power output of the engine which slows down the engine below its normal speed and decreases the power developed thereby. Under this increased load if the engine were caused to regain its normal speed it is apparent that its power would be increased to its full capacity. Slowing down of the engine on retarded throttle 1s ordinarily of little or no importance because the operator usually advances the throttle to full open position as soon as there is a substantial decrease in engine for decreasing the voltage of the generator.

Although this may be done in any suitable manner employing a speed responsive device, in the particular embodiment of my invention shown in the drawing it is done by arranging a resistance 17 in the field circuit of the generator connected across contacts 18 arranged to be bridged by a control lever 19 pivoted at 19 which is actuated by a centrifugal device or governor 20 driven by the engine 10.. The governor 20 is of the inc usual fly-ball type and is secured to its driving shaft 21 at 20 so that upon a decrease in speed of the engine a collar 20, which is slidably mounted on the shaft 21, is moved to the left along the same, thereby moving the lever 19 out of engagement with contacts 18 increasing the resistance of the field circuit and decreasing the voltage of the generator which lessens the load on the generator and increases the engine speed. In order to accelerate the increase in speed of the engine to normal an arrangement is employed for increasing the effective opening of the throttle upon a decrease in speed of the engine which takes place substantially at the same time the voltage of the generator is decreased. Obviously this may be accomplished in several diilerent ways and the particular arrangement will depend on the type of engine employed. In this instance it is done by arranging a throttle 22 in advance of the manually controlled throttle 14 which is controlled by the governor 20 through the control lever 19 and link 23 so as to be somewhat less than fully open at normal engine speed when the manual throttle is fully open. The throttle 14 is set so that it is fully opened upon movement of the lever 19 by the governor to open the circuit between contacts 18, and in this way decrease in speed of the engine is counteracted by an increase in the effective throttle opening as well as the decrease in the load on the generator.

In the arrangement illustrated, the adjustment of the governor is such as tomaintain the voltage of the generator low enough to operate the engine at the speed for maximum power only when the manual throttle is fully open. However, as previously ex plained the engine is not ordinarily overloaded when the throttle is retarded so that I prefer to connect the field resistance 17 to the throttle lever 14 and arcuate contact 14: which is arranged relative thereto in such manner that the action of the governor 20 will be ineffective to vary the resistance in the field circuit of the generator and change its voltage unless the manual throttle is substantially fully open. In some instances the characteristic of the generator may be such as to make it desirable to vary the voltage of the same at some other than fully open throttle, but under such conditions the governor 20 may readily be adjusted and the form of the arcuate contact 14* made to give the desired effect. Moreover, the governor may be controlled by a suitable mechanical connection with the throttle so as to vary the governor action throughout the range of movement of the throttle 14.

In the operation of the engine driven generator described it the manually controlled throttle 14 is retarded the lever 14 will short circuit the resistance 17 in the field circuit of the generator so that the governor 20 will not affect the voltage of the generator upon changes in speed of the engine. However, when the manually controlled throttle is fully opened, as in starting or ascending a grade, the driving motors 13 of the vehicle demand increased current and if the engine is overloaded it decreases in speed. This decrease in speed of the engine causes the governor 20 to move the lever 19 out of engagement with the contacts 18 increasing the resistance in the generator field and decreasing its voltage. The decrease in the voltage of the generator lessens the load thereon so that the engine speeds up to normal and develops its rated power on full throttle. This will cause the governor to again short circuit the resistance and decrease its speed and the decrease in speed will decrease the voltage of the generator causing the engine to again increase to normal speed. The changes in speed of the engine will successively open and close the contacts 18 by movement of the lever 19 so as to make the effective voltage of the generator such as to maintain the engine at substantially normal speed at full throttle. Successively opening and closing the contacts 18 in this manner does not cause sudden obj ectional variations in engine speed because of the damping effect of the generator field responding slowly to changes in voltage applied thereto and the inertia of the engine and rotor of the generator.

Modifications of the embodiment of my invention herein disclosed will occur to those skilled in the art, and I desire it to be understood therefore that my invention is not to be limited to the particular arrangement shown and described except as defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is-

1. In a vehicle having an engine and a. generator driven thereby, a motor connected to said generator for propelling the vehicle, an excitation system for said enerator including means for decreasing-t e voltage of the same in response to a decrease in speed of said engine, a throttle for controlling said engine, and means associated with said throttle for rendering said speed responsive means inactive to vary the voltage of said generator during a portion of the movement of said throttle.

2. In a vehicle having an engine and a generator driven thereby, a motor connected to said generator for propelling the vehicle, an excitation system for said generator including means for decreasing the voltage of the same in response to a decrease in speed of said engine, a throttle for controlling said engine, and means associated with said throttle for rendering said speed responsive means inactive to vary the volta e of said generator except when said thrott e is substantially fully open.

of said resistance to render sai 3. In a vehicle having an engine and a enerator driven thereby, a motor connecte to said generator for propelling the vehicle, an excitation system for said generator including a resistance, means responsive to a decrease in the speed of said generator forvarying said resistance to decrease the voltage of said generator in response to a decrease in speed of said engine, a throttle for controlling said engine, and means associated with said throttle for short circuitin a portion speed responsive means inactive to vary the voltage of said generator during a portion of the movement of said throttle.

In witness whereof, I have hereunto set my'hand this 9th da of January 1928.

, 'FRANKLI H. PRITdHABD. 

